I. Field of the Invention:
This invention relates to an improved method for bonding surfaces by spraying with a pressure sensitive adhesive latex. The resultant sprayed adhesive surface is characterized by the appearance of a pebbly, particulate pattern of adhesive thereby providing better efficiency of bonding, rapid and superior wet grab, as well as superior overall coverage at lower quantities for economy of use. This method is particularly effective when bonding lightweight material such as fiberglass insulation.
II. Brief Description of the Prior Art:
In many bonding applications where it is necessary to bond a porous material (e.g. fiberglass insulation, foam material, etc.) to a relatively rigid and often irregularly shaped substrate, certain unique properties, particularly a rapid "wet grab" ability, are required of the adhesive. This wet grab can usually be obtained by coating the substrate surface with an organic solvent-based adhesive and allowing the solvent to evaporate. The use of such solvents presents a number of serious problems including flammability, toxicity and attack on various substrates. Consequently, attempts have been made to achieve efficient bonding and satisfactory wet grab using latex adhesive systems. Generally these latex systems require drying after bonding in order to evaporate the water. This drying operation is particularly difficult in the case of insulation or other relatively thick substrates because it is necessary to force-dry through the entire thickness of the material. Furthermore, in the cases of these latices which must be so dried, the final degree of tack is often insufficient for the intended application and delamination occurs. Moreover, latices employed a highly viscous form and characterized by a "wet grab" due solely to their high viscosity and resulting wet cohesive strength present problems in spraying and efficient application.
It has been recognized that laminates obtained by bonding the substrates with spaced deposits of a coagulated latex adhesive produce superior laminates. Particularly in the cases wherein at least one of the substrates to be bonded is a porous material, the use of the adhesive in this coagulated particulate form has even more significance since the resultant adhesive coated surface possesses a superior degree of wet grab without the necessity for a drying operation. Certain mechanical means, such as grooved or patterned transfer rolls, have been developed to achieve this series of spaced adhesive deposits, however, the costs of the required equipment is high and the use thereof has been limited to flat or regular surfaces.
In U.S. Pat. No. 3,808,088 issued to the B. F. Goodrich Company, a bonding process has been disclosed for spraying an adhesive latex for the deposition of raised, spaced deposits. It is noted in the patent that, despite the obvious practical advantages achievable by spraying, this method of application had not been previously thought practical for use with latex based adhesive systems. Thus, it had been considered that for a binder to be sprayed it must possess a viscosity less than about 2000 cps., however, if latex adhesive droplets contact a substrate in such an unthickened state, they do not remain as discrete droplets but rather coalesce into a continuous adhesive layer and, with certain types of porous substrates, the latex is adsorbed. In order to overcome this problem, the 3,808,088 patent employs an adhesive latex containing from 0.01 to 25% carboxyl functionality. When this latex is sprayed through an atmosphere containing a volatile basic compound, the viscosity of the adhesive rapidly increases to about 10,000 cps. prior to contacting the substrate. This prior art method is relatively expensive requiring elaborate equipment to create the basic atmosphere causing health hazards and undesirable fumes concomitant with the release of these volatile components into the environment.
It is therefore desirable and the main object of this invention to provide a method for spraying an adhesive directly onto a substrate surface so as to form a particulate pattern with high wet grab characteristics without the need for elaborate equipment or specific environments.
A further object of the present invention is to provide a method for spraying latex adhesives which will produce a particulate spray pattern with a breaking of the emulsion or coagulation upon spraying and which can be employed to produce high quality laminates with little or no drying.